Underground shaft development method

ABSTRACT

An underground shaft development method comprises: (a) drilling blastholes extending into a rock formation, each drilled from a starting location defining a first blasthole end to an ending location defining a second blasthole end; (b) loading the blastholes with alternating layers of explosives charges and stemming material to provide multiple blasting decks across and within the formation, including at least a first blasting deck corresponding to the first blasthole ends and a final blasting deck corresponding to the second blasthole ends, wherein each blasting deck carries wireless blasting devices; and (c) detonating the explosive charges in a series of blasting stages based on blasting deck by initiating the wireless blasting devices in each blasting deck, proceeding consecutively from the first blasting deck to the final blasting deck, wherein after each blasting stage excavation takes place to progress the shaft in an intended direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of the specification of Singapore Patent Application No.10201703958T is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method for shaft development or shaftsinking in rock formations.

BACKGROUND OF THE INVENTION

Shafts are a core feature in many civil engineering and miningoperations. Shafts are typically required for movement of personnel,equipment, materials and water, and for ventilation purposes. Shaftsinking (or shaft mining) refers to the process by which a shaft isdeveloped. Shaft sinking in rock formations is typically undertaken by aprocess in which the shaft is lengthened in a series of stages. Eachstage involves drilling rounds of blastholes in a predeterminedarrangement, loading the holes with explosives, and blasting. Aftersuitable ventilation, rock is excavated from the area blasted and groundsupport installed as necessary. The next stage of drilling, blasting,excavation, and ground support installation is then carried out, and soon in a repeated manner. Thus, the shaft is extended in each stage.

This conventional process has a number of limitations and disadvantagesassociated with it. The process is very labour intensive and potentiallyhazardous. For example, drilling of blastholes and loading of explosivesinto blastholes per stage is a manual process requiring personnel towork in the shaft for many hours at a time. The shaft is developed overrelatively small distances per drilling cycle, and the drillingequipment used is relatively small and often hand-operated. Typically,the blastholes will have a diameter 38-64 mm and their length perdrilling cycle will be restricted to between 0.5 and 3.0m.

The present invention seeks to provide a new approach to shaft sinkingthat provides benefits when compared with the conventional blastingapproach discussed.

SUMMARY OF THE INVENTION

Accordingly, in accordance with an aspect of the present disclosure, amethod of sinking a shaft in a rock formation comprises: drillingblastholes extending into the formation, the blastholes having a top endand a bottom end; loading the drilled blastholes with alternating layersof explosives charges and stemming material to provide a series ofblasting decks extending across and within the formation; and initiatingthe explosive charges in a series of blasting stages based on blastingdeck and proceeding consecutively from the blasting deck located at thetop of the blastholes to the blasting deck located at the bottom of theblastholes, wherein after each blasting stage, excavation takes place toprogress the shaft in an intended direction.

In accordance with another aspect of the present disclosure, a method ofsinking a shaft in a rock formation comprises: during a selected shaftdevelopment interval: (a) drilling blastholes extending into theformation, each blasthole drilled from a starting drilling locationdefining a first end of the blasthole to an ending drilling locationdefining a second end of the blasthole such that the blasthole has adepth between its first end and second end; (b) loading the blastholeswith alternating layers of explosives charges and stemming material toprovide a series of blasting decks extending across and within theformation, including at least first blasting deck corresponding to thefirst ends of the blastholes and a final blasting deck corresponding tothe second ends of the blastholes, wherein each blasting deck includeswireless blasting devices; and (c) detonating the explosive charges in aseries of blasting stages based on blasting deck by way of initiatingthe wireless blasting devices in each blasting deck, proceedingconsecutively from the first blasting deck corresponding to the firstends of the blastholes to the final blasting deck corresponding to thesecond ends of the blastholes, wherein after each blasting stagecorresponding to the selected shaft development interval, excavationtakes place to progress the shaft in an intended direction.

In some embodiments, the series of blasting decks extending across andwithin the formation includes at least three blasting decks, includingat least one blasting deck disposed between the first blasting deck andthe final blasting deck.

In some embodiments, in the selected shaft development interval thedepth of each blasthole is between 10-80 m. In other embodiments, in theselected shaft development interval the depth of each blasthole isgreater than 80 m.

Depending upon the direction of shaft development, the final blastingdeck will be deeper within the earth than the first blasting deck (shaftdevelopment having a downward directional component), or the finalblasting deck will be closer to the surface of the earth than the firstblasting deck (shaft development having an upward directionalcomponent). The shaft can be developed to intersect an undergroundexcavation (e.g., an existing underground passage or tunnel).

In the selected shaft development interval, the wireless blastingdevices in each blasting deck can be programmed with a unique groupidentifier corresponding to the blasting deck.

In accordance with a further aspect of the present disclosure, themethod further comprises: during an additional shaft developmentinterval following the selected shaft development interval, repeatingsteps (a) through (c), wherein after each blasting stage correspondingto the additional shaft development interval, excavation takes place toprogress the shaft in an intended direction.

In the additional shaft development interval, the depth of eachblasthole can be between 10-80 mm, or longer than 80 m depending uponembodiment and/or situational details.

In the additional shaft development interval, the wireless blastingdevices in each blasting deck can also be programmed with a unique groupidentifier corresponding to the blasting deck.

Throughout this specification and the claims which follow, unless thecontext requires otherwise, the word “comprise”, and variations such as“comprises” and “comprising”, will be understood to imply the inclusionof a stated integer or step or group of integers or steps but not theexclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (orinformation derived from it), or to any matter which is known, is not,and should not be taken as an acknowledgment or admission or any form ofsuggestion that prior publication (or information derived from it) orknown matter forms part of the common general knowledge in the field ofendeavour to which this specification relates.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are illustrated in the accompanyingnon-limiting drawings in which:

FIG. 1 is an illustration showing the steps associated with each stageof a conventional shaft sinking technique;

FIG. 2 is a schematic illustrating a conventional shaft sinkingtechnique;

FIG. 3 is an illustration showing the steps involved with stages of themethod of the present invention; and

FIGS. 4-7 are schematics illustrating the shaft sinking method of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention involves drilling of blastholes and loading ofblastholes with explosives charges and stemming material in a singleevent. The explosives charges and stemming material are provided in theblastholes to provide blasting decks within and across the rockformation into which shaft sinking takes place. The blasting decksdivide the rock formation into rock volumes/regions that will be blastedin a stage-wise approach. Each blast will break rock in the immediatevicinity of the relevant explosives charges and the broken rock is thenexcavated before the explosive charges in the next blasting deck areinitiated, and so on.

Key differences between the present invention and the conventionalapproach can be explained with reference to FIGS. 1-4.

With respect to FIG. 1 a conventional shaft sinking technique in a rockformation involves a repeated cycling of the following steps:

-   -   drilling blastholes    -   charging blastholes with explosives    -   blasting (and ventilating the area)    -   excavating rock from the area blasted    -   installing ground support

By following this approach, a shaft will be developed by approximatelythe length of the blastholes per cycle. In practice this length will beup to about 3 m.

FIG. 2(a)-(g) shows steps involved in the conventional shaft sinkingtechnique, consistent with FIG. 1. In FIG. 2(a) blastholes are drilledin accordance with a predetermined pattern to define an area in which ashaft is to be formed. The blastholes are loaded with explosives andblasted (not shown). FIG. 2(b) shows an excavator removing blasted rockthereby commencing shaft sinking. In FIG. 2(c) new blastholes aredrilled and loaded with explosives, and blasted (not shown). FIG. 2(d)shows excavation of blasted rock and extension of the shaft in adownward direction. These steps are repeated in FIG. 2(e)-(g) therebydeveloping a shaft. The Figures do not show installation of any groundsupport, but this will invariably take place after each cycle ofdrilling, loading, blasting and excavating.

With respect to FIG. 3, the method of the present invention involves oneor more shaft development time periods, intervals, iterations, orcycles, where for a given shaft development time period, interval,iteration, or cycle under consideration, the method includes drillingblastholes and loading the blastholes with multiple layers of explosivecharges corresponding to multiple blasting decks in a single blastholedrilling and loading event or procedure. Thereafter, within the currentshaft development time period, interval, iteration, or cycle, the methodinvolves repeated cycling of the following steps:

-   -   blasting (and ventilating the area);    -   excavating rock from the area blasted; and    -   installing ground support        until no more blasting decks along the depth of the blastholes        drilled during the current or most-recent shaft development time        period, interval, iteration, or cycle are available for        blasting. Depending upon embodiment and/or situational details,        after completion of the shaft development iteration or cycle        under consideration, another or subsequent shaft development        time period, interval, iteration, or cycle can be performed,        e.g., on a selective basis depending upon whether a target        overall shaft length or depth or target overall shaft        destination has been reached or realized.

By following this approach, the need to carry out drilling and loadingexplosives after each stage of excavation is eliminated. That is, thepresent invention eliminates the conventional requirement to carry outblasthole drilling and explosives loading corresponding to a next shaftlevel or shaft depth increment to be blasted after each excavation ofthe most recent shaft level that was blasted. Rather, a single blastholedrilling and explosives loading event or procedure is performed thatphysically or spatially encompasses or defines multiple blasting decksalong the depth of the blastholes, where each blasting deck (a)corresponds to a particular shaft level or shaft depth increment, and(b) includes explosive charges that have been pre-positioned atpredetermined depth(s) within the blastholes during the single blastholedrilling and loading event or procedure. Following the single blastholedrilling and explosives loading event or procedure spanning multipleblasting decks corresponding to multiple shaft levels or shaft depthincrements, individual blasting decks across these multiple blastingdecks can be sequentially or consecutively blasted and excavated toprogressively extend the depth of the shaft.

The method of the invention involves a single drilling and explosivesloading stage of multiple relatively long blastholes, which means thatlarger scale, automated equipment may be used. Typically, the blastholediameter may be 76-165 mm and the blasthole length or depth may be atleast 10-20 m, for instance, 25-30 m or longer (e.g., 80 m). Even thoughin various embodiments the blasthole depth is between 10-80 m, it may bepossible to drill to depths more than 80 m (e.g., up to 100 m, 120 m,150 m, 180 m, 200 m, 220 m, or 250 m) depending upon the characteristicsof the rock formation and the sophistication of the drilling equipmentbeing used. Contrast this with the conventional approach where multipledrilling stages of relatively short blastholes is necessary.

FIG. 3(a)-(e) shows steps involved with the method of the presentinvention, consistent with FIG. 2. In FIG. 3(a), blastholes are drilledin accordance with a predetermined pattern to define a region or area inwhich a shaft is to be formed. The blastholes extend over the fulllength of the proposed shaft corresponding to a particular shaftdevelopment time period, interval, iteration, or cycle. The blastholesare loaded with explosives charges and stemming material to provide aseries of blasting decks, i.e., multiple blasting decks. For shaftdevelopment along a downward direction (e.g., away from the surface ofthe earth), explosives charges in the blasting deck at the top of theblastholes are then initiated, thereby breaking rock in the immediatevicinity. This broken rock is then excavated as shown in FIG. 2(b).Undetonated explosive charges are slept. After this excavation, theexplosive charges in the next blasting deck down are initiated andbroken rock excavated, and so on, as shown in FIGS. 2(c), (d) and (e).For purpose of brevity and simplicity, the Figures do not showinstallation of any ground support, but this will take place after eachcycle of excavation in a manner readily understood by individuals havingordinary skill in the relevant art.

A key feature of the present invention is that it minimises the stepsinvolved in sinking a shaft over a given distance. For example, usingthe conventional approach to extend a shaft over 30 m could require 10or more cycles of drilling and explosives loading. In contrast, usingthe present invention the same may be achieved in a single event ofdrilling and explosives loading. Depending upon the desired targetoverall depth of the shaft and the characteristics of the rockformation, the method of the invention may be applied to sink a shaft toits target overall depth in association with a single shaft developmenttime period, interval, or iteration. However, if this is not possible,the method of the invention may be repeated across multiple shaftdevelopment time periods, intervals, iterations, or cycles to developthe shaft to its intended target overall depth. For example, if theintended target overall shaft depth is 100 m or greater, the shaft maybe developed by applying the method of the invention over multiple(e.g., 2 or more) shaft development time periods, intervals, iterations,or cycles.

The invention requires loading of blastholes with a plurality ofexplosive charges and the selective, sequential initiation of thosecharges, such that charges in a first deck (e.g., an uppermost or topdeck) or a deck directly adjacent to a current excavated blasthole depthare detonated, while charges in other decks that are deeper relative tothe blasthole's depth (e.g., decks below the uppermost or top deck,correspondingly) are slept. Herein, reference to loading blastholes withexplosive charges means that blastholes are loaded with explosiveformulations and initiation systems, in a manner that will be readilycomprehended by individuals having ordinary skill in the relevant art.The initiation systems used in a given blasting deck will need to remainoperational and unaffected by the initiation of explosives formulationsin previously blasted decks in the same blasthole and in adjacentblastholes. This effectively precludes the use of wired initiationsystems that rely on cables for communication of command signals. Suchcables will most likely be compromised by blasts within the sameblasthole and/or in adjacent blastholes. This issue may be addressed inaccordance with the present invention using a wireless electronicblasting system (WEBS) to initiate explosives formulations.

The WEBS is an electronic initiation system suitable for initiation ofexplosive charges. The WEBS includes multiple wireless blasting devices(e.g., wireless explosive primers), each of which is powered by anenergy source (e.g., an internal (on-board) energy supply such as abattery), and each of which receives command instructions wirelessly,for example, by way of very low frequency magnetic resonance signalsthat can be transmitted through rock, air and/or water. The WEBS doesnot rely on any physical (wired) connections to an external power supplyor to a blasting machine for communications necessary for blastingfunctionality (e.g., issuing FIRE commands to WEBS blasting devices). Inthe context of the present invention, this means that blasting horizonswill not be damaged by preceding blasts and communication channels toeach WEBS blasting device will remain intact. In the WEBS, individualblasting devices can also be programmable with respect to WEBSgroup/subgroup identity and/or detonation delay time, and this willenhance implementation of the invention as will be discussed.

Suitable WEBS and corresponding WEBS blasting devices for use in thepresent invention are known and described for example in Applicant's ownInternational Patent Publication No. WO2015/143501 and InternationalPatent Publication No. WO2015/143502, the contents of which areincorporated herein by reference. Suitable WEBS are commerciallyavailable through Orica International Pte Ltd., Singapore.

Additional aspects of the invention will be elaborated upon withreference to FIGS. 5-7.

FIG. 5 illustrates a series of 8 vertical blastholes. Each blasthole isloaded with explosives charges and stemming material (inert horizon).The explosives charges and stemming material are arranged in a series ofblasting decks denoted Blast 1, Blast 2 . . . Blast X+2. In variousembodiments, in a given blasting deck, the explosive charges andstemming material are at approximately the same depth, and extend overapproximately the same length within the blastholes.

A layer of stemming material (e.g., graded rock gravel) covers theexplosive charge(s) in any given deck, where such stemming material isintended to prevent transmission of explosives energy to an adjacentblasting deck. Using the nomenclature of FIG. 5, the blasting deckdenoted Blast 1 is blasted first, followed by excavation of broken rockand installation of ground support as required. Thereafter, the blastingdeck denoted Blast 2 is blasted (followed by excavation of broken rockand installation of ground support as required), and so on untilblasting deck denoted Blast X+2 is blasted. During a blast directed to acurrently selected deck, and in between blasts, remaining explosivecharges corresponding to other decks in the blasthole (i.e., explosivecharges in decks deeper relative to the depth of the blasthole than thecurrently selected deck) are slept. Once rock broken by the mostrecently blasted deck has been cleared and ground support installed, anext sequential deck in the blasthole (i.e., the next deeper deckrelative to the depth of the blasthole, directly adjacent to themost-recently blasted deck) can be blasted.

After each blasting deck has been fired it is not essential for thefloor of the developing shaft to be cleared or cleaned completely beforethe next blasting deck is fired, since there is no need to undertake anyfurther drilling and explosives loading that would otherwise necessitatea suitably cleared or clean floor for effective operation of equipmentand safety of personnel.

The length of rock blasted in each blasting deck may vary depending uponsuch things as:

-   -   the geological and geotechnical conditions;    -   the blasthole design (density and pattern of holes, burden, and        relief);    -   the initiation sequence (e.g., the inter-deck and/or intra-deck        initiation sequence);    -   the explosives type/types and energy/energies; and/or    -   restrictions on blast induced ground vibration and/or noise

FIG. 6 shows a typical arrangement of blastholes for a shaft. In theembodiment shown, the blastholes are arranged in concentric rings arounda central relief hole. The use of a relief hole may not be essential,but it can be useful in providing vacant space for broken rock to moveinto during the various blasts that will take place.

The outer ring of blastholes are intended to define the outer walls ofthe shaft. Blasts in this outer ring may take place with a lower volumeof explosives and/or lower energy explosives to ensure that excessivedamage does not occur in the rock that will form the outer walls of theshaft. The explosive charges in blastholes in the outer ring may beinitiated at the same time as other explosives charges within the sameblasting deck. Preferably, however, the explosive charges in the outerring of blastholes are initiated before the other explosives charges inthe same blasting deck as this may lead to less overall damage to thewalls of the shaft. It will be appreciated that the blastholes in theouter ring are typically pre-split blastholes.

The remaining blastholes may be arranged in any suitable pattern toachieve suitable breakage of rock in the vicinity of the blasthole. Thecharacteristics of the rock formation and the nature of the explosivesformulations being used will influence the grouping and/or density ofblastholes used.

The explosives in each blasting deck are initiated completelyindependently of explosives in other blasting decks. Within the sameblasting deck, the explosives charges may be initiated at the same timeor with delay times relative to each other. The latter may be preferredin terms of blasting effectiveness. As explained, blastholes that are atthe boundary of the shaft (pre-split blastholes) may be initiated beforeother blastholes within the same blasting deck. This may provide reliefat the perimeter of the shaft and minimise wall damage.

To achieve suitable initiation control of explosives formulations theWEBS blasting devices in the same blasting deck may bfse allocated aunique group identifier that ensures that only wireless commands(including FIRE commands) intended for those WEBS blasting devices areactioned. This approach allows each WEBS blasting device being used tobe programmed before or on deployment in a blasthole to enhanceeffectiveness and efficiency of operation. This approach also allows aspecific (predetermined) group of WEBS blasting devices to be detonatedin a desired sequence, while other pre-programmed WEBS blasting devicesdo not initiate. Rather, those WEBS blasting devices sleep in theblastholes until they are commanded by a suitably coded signal to wakeup and detonate. The use of group identification features to ensure thatcommand signals are actioned by a predetermined group of wirelessdevices is the subject of International Patent Publication No.WO2010/085837, the contents of which are incorporated herein byreference.

FIG. 7 shows the blastholes, explosives charges and stemming materialfrom a different perspective. In this figure, wireless electronicprimers are used as the WEBS blasting devices.

The explosives formulations used will be of known composition and willbe selected based on their suitability for the shaft sinking situationunder consideration. Typically, the explosive formulation will be anemulsion explosive formulation.

When ground support is required, conventional components andmethodologies will be used; including rock bolts, wire mesh andpre-formed concrete shaft liners. Individuals skilled in the art will befamiliar with the appropriate ground support to use, depending oncontext.

The present invention may be applied to “Conventional Shaft Sinking” andto “Rise Mining”. In “Conventional Shaft Sinking” the free or accessiblesurface is initially at the top of the blastholes, with shaftdevelopment extending downwards. The shaft produced is usually verticalor just off vertical (by up to about 15° for example). In the invention,broken rock is excavated using conventional shaft sinking diggingapparatus, such as cactus grabs and bucket excavators or manually usingshovels. Each subsequent layer of rock is blasted only when enoughbroken rock has been removed so that the next blast remains unaffected.

The method may also be applied to “Rise Mining,” e.g., where the shaftblastholes have been designed to intersect an underground excavationsuch as an existing underground passage or tunnel. In this case, thefree or accessible surface is initially at the bottom of the blastholes,and shaft development proceeds upwards. When the invention is used forRise Mining, broken rock that results from blasting a given deck fallsunder gravity and can be removed, for example by mechanical loadingmachines (i.e., front end loaders). A subsequent blasting deck can beblasted when there is enough space beneath the blast to allow the newlybroken rock to expand into it.

In a variation of this, the method of the invention may be applied toproduce drawbells in a block cave mining operation. In this case thefree or accessible surface is again at the bottom and removal of rockproceeds upwards. As rock is broken it falls under gravity and may beremoved. Applying the method of the invention to produce drawbells mayallow larger sized drawbells to be produced when compared with singleshot production techniques. This is because in accordance with theinvention, rock may be blasted and removed incrementally in controlledvolumes based on blast design.

1. A method of sinking a shaft in a rock formation, comprising: during aselected shaft development interval: (a) drilling blastholes extendinginto the formation, each blasthole drilled from a starting drillinglocation defining a first end of the blasthole to an ending drillinglocation defining a second end of the blasthole such that the blastholehas a depth between its first end and second end; (b) loading theblastholes with alternating layers of explosives charges and stemmingmaterial to provide a series of blasting decks extending across andwithin the formation, including at least first blasting deckcorresponding to the first ends of the blastholes and a final blastingdeck corresponding to the second ends of the blastholes, wherein eachblasting deck includes wireless blasting devices; and (c) detonating theexplosive charges in a series of blasting stages based on blasting deckby way of initiating the wireless blasting devices in each blastingdeck, proceeding consecutively from the first blasting deckcorresponding to the first ends of the blastholes to the final blastingdeck corresponding to the second ends of the blastholes, wherein aftereach blasting stage corresponding to the selected shaft developmentinterval, excavation takes place to progress the shaft in an intendeddirection.
 2. The method of claim 1, wherein the series of blastingdecks extending across and within the formation includes at least threeblasting decks, including at least one blasting deck disposed betweenthe first blasting deck and the final blasting deck.
 3. The method ofclaim 1 or 2, wherein in the selected shaft development interval, thedepth of each blasthole is between 10-80 m.
 4. The method of claim 1 or2, wherein in the selected shaft development interval, the depth of eachblasthole is greater than 80 m.
 5. The method of any one of claims 1-3,wherein the final blasting deck is deeper within the earth than thefirst blasting deck.
 6. The method of any one of claims 1-3, wherein thefinal blasting deck is closer to the surface of the earth than the firstblasting deck.
 7. The method of claim 1 or 2, wherein the shaft isdeveloped to intersect an underground excavation.
 8. The method of claim1, wherein in the selected shaft development interval, the wirelessblasting devices in each blasting deck are programmed with a uniquegroup identifier corresponding to the blasting deck.
 9. The method ofclaim 1, further comprising: during an additional shaft developmentinterval following the selected shaft development interval, repeatingsteps (a) through (c), wherein after each blasting stage correspondingto the additional shaft development interval, excavation takes place toprogress the shaft in an intended direction.
 10. The method of claim 9,wherein in the additional shaft development interval, the depth of eachblasthole is between 10-80 m.
 11. The method of claim 9, wherein in theadditional shaft development interval, the depth of each blasthole isgreater than 80 m.
 12. The method of claim 9, wherein in the additionalshaft development interval, the wireless blasting devices in eachblasting deck are programmed with a unique group identifiercorresponding to the blasting deck.